Conventional power amplifiers function as voltage regulators that use a programmable regulating element (e.g., a power transistor) in a series circuit comprising a power supply, the element itself and a load. A disadvantage of this approach is that all load current must pass through the regulating element. When large amounts of current are required, single regulating elements are not adequate to the conductive task and multiples of the series connected regulating element are ganged or connected in parallel to satisfy the demand for current. This format requires precise equalization of the current flows through the ganged elements to prevent disproportionate stress on any one of the ganged elements.
This equalization of current flows through ganged elements exacts a high cost from the power efficiency of the overall system. In order to enhance the system efficiency, it is known to provide multiple voltage levels for the amplifier supply rails, with the higher levels being switched in as clipping becomes imminent at each preceding lower voltage level. Other series-type designs strive to provide a continuously variable supply rail in synchronous proportion to the demand represented by a low-level input signal. In addition to suffering from narrow frequency constraints and substantial power limitations, these designs retain a series flow of power through the regulating element. In most systems, these regulating elements are the single most significant limiting factor in improving overall system efficiency.